What approaches to the exploration of Mars will maximize the astrobiological science return? The astrobiology science goals for Mars are extremely broad, and it can be argued that virtually any mission can return data of relevance to issues relating to the habitability of Mars. However, consideration of the data from past and current Mars missions and expectations for those currently in development for launch during the 2007 and 2009 opportunities suggest that the greatest increase in understanding of Mars will come from the collection and return to Earth of a well-chosen suite of martian surface materials. Given the Mars Exploration Rover experience and current understanding of the nature of materials on the martian surface, a "grab sample" obtained from a stationary lander is not likely to be sufficient to provide the necessary data.
Finding. Sample return should be seen as a program that NASA and the Mars science community have already embarked upon rather than as a single, highly complex, costly, and risky mission that is to occur at some future time.
Recommendation. The highest-priority science objective for Mars exploration must be the analysis of a diverse suite of appropriate samples returned from carefully selected regions on Mars.
Programmatically, sample return should be phased over three or more launch opportunities. That is, samples can be collected and cached on Mars by one or more missions. A selected cache can be retrieved by a subsequent mission and launched into orbit about Mars for collection and return to Earth at a later date. Sample caching could be carried out by each surface mission, utilizing a minimalist approach so as not to make sample caching a cost-or technology-driver. Such a strategy, accompanied by a reduction in the size of the landing error ellipse, should allow collection of diverse samples and mitigate the costs of sample-return missions.
Irrespective of the compelling scientific arguments for the return of martian samples to Earth, the implementation of a sample-return mission will be a technically challenging, high-risk, high-cost endeavor. Because it will be comparable in expense to the highest-priority activities proposed by other scientific communities, the decision to implement a Mars sample-return mission will hinge on factors beyond the scope of this study. As such, it behooves the astrobiology community to plan for the possibility that a Mars sample-return mission is not an integral component of current mission plans.
Recommendation. If it is not feasible to proceed directly toward sample return, then a more gradual approach should be implemented that involves sample caching on all surface missions that follow the Mars Science Laboratory, in a way that would prepare for a relatively early return of samples to Earth.
If a commitment is not made for sample return, then high-priority, astrobiologically relevant science still can be done on Mars with missions such as the Astrobiology Field Laboratory or the Mid Rovers, provided that they are instrumented appropriately. However, it must be recognized that the ability of these missions to make fundamental discoveries is much more limited than would be the case with a sample-return mission.
International collaboration has the potential to make expensive undertakings such as a Mars sample-return mission affordable. But the benefit has to be balanced against the political difficulties of working with multiple countries and multiple space agencies.
Recommendation. International collaboration in Mars missions should be pursued in order to make expensive missions affordable, especially in the areas of sample caching and sample return.
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